1. Field of the Invention
The invention relates to heating devices for fixing toner onto a copy sheet. More particularly, the invention relates to a flash fusing device for fixing the toner.
2. Prior Art
The use of flash fusing devices for fusing toner particles adhering to a latent electrostatic pattern on a dielectric recording medium, such as paper sheets, is well known in the prior art. Such a flash fusing device consists of a reflector which directs radiation generated from a flash lamp onto the surface of the recording medium carrying the toner particles. The energy associated with the radiation is of sufficient magnitude to heat the toner into a molten state while the characteristics of the recording medium are substantially unaffected.
The molten toner penetrates into the fiber of the recording medium. Upon subsequent cooling, the toner image becomes indelibly fixed into the medium to form a permanent copy.
U.S. Pat. No. 3,445,626 to Thomas B. Michaels exemplifies the prior art fusing devices. The Michaels' patent describes a fusing assembly consisting of a xenon gas lamp and reflector assembly. The lamp and reflector are arranged in a conventional manner and disposed relative to a copy sheet transport device. A paper sensing device is disposed at the entry side of the fusing assembly. As a sheet is transported under the xenon lamp/reflector assembly, the leading edge of the sheet activates the sensing device and a signal is generated therefrom. The signal initiates a timing circuit to permit movement of the detected sheet or card to a second position relative to the fusing assembly, at which time the flash lamp is triggered to fix the toner pattern on a section of the card. A logic interlock circuit permits the flash lamp to remain untriggered in the absence of any card to be fused. The interlock circuit also provides for successive triggering of the flash lamp in order to fuse an entire card.
U.S. Pat. No. 3,871,761 is another example of the prior art flash fuser. The fuser consists of a flash lamp mounted within the cavity or interior of a radiation reflector. The reflector and the flash lamp are mounted above a paper transport. A copy sheet carrying a toned image is advanced under the fuser by the paper transport. As the sheet passes under the fuser, the flash lamp is repeatedly triggered. By triggering the flash lamp repeatedly, a plurality of flashes are generated. The plurality of flashes are used to fuse the toned image onto the copy sheet.
U.S. Pat. No. 4,121,888 describes another prior art flash fuser. In this system a single flash is utilized for fixing toner onto a copy sheet. The fuser consists of a flash lamp mounted within a reflector. The opening of the reflector faces a copy sheet paper path. Copy sheets carrying toned images are transported along the paper path. The dimension of the opening is equivalent to the dimensions of a conventional or typical copy sheet. As such, when a copy sheet is aligned with the opening, a single flash from the flash lamp fuses the entire sheet. Sensor means is provided to activate the flash lamp when the sheet is positioned in proper alignment with the opening. The flash is initiated by a triggering circuit. A power supply charges a capacitor which supplies energy to sustain the flash.
One of the main problems associated with the prior art flash fusers is that the power supplies are unduly large, bulky and expensive to manufacture. Usually these large power supplies require a relatively large quantity of energy.
As is well known, the flash fuser is one of the plurality of elements used in an electrophotographic copier. As such, the flash fuser, power supply, charging and triggering circuits are housed in the frame of the copier. The miniaturization of copiers appears to be the trend for copier designers. There is also a requirement that miniature copiers be low cost and utilize a relatively low quantity of energy for operation. Due to the bulkiness and high cost of the prior art power supplies, they are not suitable for use in miniaturized copiers.
Even in stand-alone (large size) copiers, the use of flash fusing appears to be restricted. It is believed that the restrictive use stems from the adverse characteristics of the power supply.
As is evident from the above description of the prior art, either a single flash is used to fuse a page or multiple flashes are used to fuse a single page. In either case, a single flash fuser device (that is a reflector and a flash lamp) is used to generate the flashes. When a single flash is used, the effective fusing area must be at least equivalent to the size of the sheet. Needless to say that as the size of the sheet increases, the effective fusing area and hence the energy requirement of the fusing system increases. In order to meet the high energy requirement in a single flash system, the power supply, charging capacitor and related electrical circuits and/or components must be increased accordingly. In order to generate a fixed number of copy sheets per unit time, a sheet must be fused within a relatively short period of time, say a fraction of a second.
Generally, the rating of electrophotographic copiers is based on the number of copies that are generated per unit time. To meet a particular rating or throughput, the fuser must fix a certain number of copies per unit time. By way of example, if minute is the per unit time for copier rating, then second is the per unit time for fuser rating. In order to meet this rating, when multiple flashes are used to fix a copy sheet, the frequency of this flash is relatively close. This means that the time interval between flashes is relatively short. As was stated previously, each flash fuser requires an energy supply source to supply energy to the flash lamp. Usually, the energy supply source includes a power supply and an energy storage device such as a capacitor. The capacitor dumps stored energy into the flash lamp while the power supply charges the capacitor. Obviously, the shorter the time interval between flashes, the more powerful a power supply is needed. In order to be sure that the necessary energy is available to charge the capacitor within the relatively short time interval, the power supply is over designed. This leads to the unusually large size power supplies which are used with prior art flash fusing assemblies.